M94 transmission - "factory" or traumatic groove in gear?

[genen8kua]

This is a photo through the transmission oil fill opening on my R1100RT which has 52K miles. Note the little slightly angled cuts in the two visible teeth. The rest of the gear surface looks smooth: the other apparent irregularities in the photo are flash artificats/reflections in the oil film.

Somewhere at 25Kmiles or so, the previous owner had the bad M97 transmission replaced with a used M94. I don't know how many miles there are on the transmission. It works fine.

About 3000 miles ago I changed the transmission oil for the first time since I've owned the bike. It had been changed 6,000 prior (per service records) and when I changed it the oil came out extra dark (maybe a bearing seal opened?).

I did a couple of short interval oil changes & after maybe one change where the oil came out a bit darker than when it went in, it doesn't seem to be changing. I also haven't seen the irridescent gold sheen of wearing shift forks as described on the largiader.com website.

I noticed the "groove" in the gear (I think it's 5th) on that first oil change and it looked pretty uniform, so I really didn't think much about it. But I also read up on the transmissions and while it looks like sometimes lubrication grooves are cut in gears, I don't see such on photos of the oilhead transmissions I've seen.

So it has me wondering. The groove on the gear is quite a uniform cut, a mm or two deep and the same on every tooth. So if some stray piece of metal got stuck in place and did damage, it did it awfully uniformly. (But the mere existence of an apparent design doesn't prove there was a designer!) No metal chuniks in the oil or on the magnetic plug. A little fine sludge.

I'm hoping someone can tell me "oh yeah, mine has that," or even confirm it was a feature of at least some of the M94 transmissions.

It shifts consistently through all gears. The only hiccup was about 9,000 miles ago when the bike was relatively new to me and (once and only once) it popped out of 5th gear - I was new to the bike & figured I must not have gotten it in gear all the way. That has never repeated itself.

If not "factory", then I guess I'm looking for opinions on what to do next. It's hard to embark on a rebuild of something that's working fine, but 3000 miles ago I'd figured a problem if present might manifest itself & I could deal with it over the winter when I wouldn't be riding as much anyway. I'm thinking this might be a case where an oil analysis could be reassuring if it doesn't show evidence of abnormal wear. I and my pocketbook would like to just keep doing regular tranny oil changes and stop worrying about it unless it starts to act up. Thoughts?

Thanks in advance!

 

[jingdog]

As long as the transmission is shifting normally it should continue to do so. The classic problem with these things is popping out of gear. Along with mocha colored oil. (which as I understand it is associated with bad bearings) Yours is doing neither. Those marks might be something that happened during the manufacturing process. (Remember, BMWs are like sausages: tasty but dont watch them being made!) Or post manufacturing. Doesnt really matter it works. If this was a tractor on the farm youd leave it running until it did otherwise.

 

[genen8kua]

As long as the transmission is shifting normally it should continue to do so. The classic problem with these things is popping out of gear. Along with mocha colored oil. Yours is doing neither. Those marks might be something that happened during the manufacturing process. (Remember, BMWs are like sausages: tasty but dont watch them being made!) Or post manufacturing. Doesnt really matter it works. If this was a tractor on the farm youd leave it running until it did otherwise.

Thanks & good point about the gear, though I did get the mocha colored oil - (if the attached is what folks talk about) hence the short interval oil changes (and it's not continuing). So I'm not entirely without worries! But, right, not popping out of gear.

 

[jingdog]

Hmm I have to say that does not look like mocha oil. Mocha oil is really BROWN. That just looks a little dark. Have you read Anton L's transmission internet article? Comparing that to what you describe I dont think you have a problem. That oil doesnt look brown enough and the tranny isnt popping out of gear. My 96 GS had the tranny go on the PO's dime. I talked about it with him quite a bit before I bought the bike. He said his oil was brown like mocha coffee brown and the transmission "skipped" in second (or third?) gear.
As long as it doesnt skip I think its good.

 

[MCMXCIVRS]

That sort of groove is pretty common on gears. Something in the machining process I imagine. I don't think it serves any purpose, or at least none that I'm aware of, but certainly is normal and does no harm.

The gears are very hard and any damage would be much more irregular; more like chips and pieces broken out.

 

[jingdog]

That sounds right to me about what dammaged gears look like. Theres chips and irregular shapes. Your shapes are symetrical.

 

[AntonLargiader]

Gene, the groove is totally normal.

The oil might be a problem; I can't really see it that well.

 

[genen8kua]

Gene, the groove is totally normal.

The oil might be a problem; I can't really see it that well.

Thanks, Anton - good to know on gear - it looked too regular to be something that wasn't cast in. Having split exactly zero trannies myself...

The dark oil is a bit of a puzzle. 6000 miles before the photo, according to records, both the FD and transmission oil were changed with BMW gear oil. When I changed it, clean red oil came out of the FD and much darker oil from the transmission. To my nose, it didn't smell different from other gear oil (not burnt-smelling) & there also wasn't a coppery-gold sheen. I was worried about a bearing's becoming unsealed & did a couple of short interval (500 or so) oil changes which looked pretty much the same coming out as going in.

So I wonder if there was old moly or something left in the transmission, or maybe the records weren't quite right. The transmission shifts well in all gears.

Thanks all for the input!

My current plan is to do my best not to worry about it & maybe re-change the gear oil after another 3K. Maybe I'll send in a sample for an oil analysis sometime down the road. The transmission replacement and new clutch were done at 28.7K and I've just turned over 52K. Sooner or later I'll need to do a clutch spline lube, but probably not yet.